1. Field of the Invention
The present invention relates to a recordable optical disk having a plurality of recording layers in a laminated direction, and to an optical disk apparatus preferably used for the disk.
2. Disclosure of the Related Art
Currently, Blu-ray disks (hereafter, “BD”) are commercially available as a large capacity recording medium. A recordable type of BD enables 25-gigabyte data recording in a single layer and 50-gigabyte data recording in two layers. By increasing the number of recording layers included in a single BD, it is possible to further increase the recording capacity.
The following steps may be employed when forming a plurality of recording layers in a BD.
(1) Injection molding is used to form an undulating shape in a first layer (recording layer L0) on a substrate;
(2) A reflecting film is formed by sputtering on the formed undulating shape;
(3) A UV resin is coated on the reflecting film (intermediate layer);
(4) A stamper having an undulating shape for a second layer (recording layer L1) is pressed into contact with the UV resin;
(5) The UV resin is cured by irradiation with ultraviolet radiation, and thereafter, the stamper is drawn and peeled off;
(6) A diffusion shell on the UV resin is formed by sputtering;
(7) The steps (3) to (6) are repeated according to the number of recording layers;
(8) A UV resin is coated on the diffusion shell (cover layer); and
(9) The UV resin is cured by irradiation with ultraviolet radiation.
In substitution of the steps (8) and (9), a technique of forming a cover layer by adhering a sheet formed from polycarbonate can be used.
In this manner, when disposing a plurality of recording layers on a single BD, it is necessary to repeat the steps such as sputtering, coating of UV resin, and curing for a plurality of number of times.
When disposing a plurality of recording layers in a BD, considerable defects may occur in the recording layers due to unacceptable decentering in the tracks on the recording layers during the step of manufacturing the disk. Conventionally, when a considerable defect is present in even one of a plurality of recording layers, that disk is discarded as a defective article. However, as a result, the manufacturing costs associated with the discarded disks are lost and also waste of materials is caused.